4L80E TCC unlocking when it shouldn't

[Oldude]

So my 1999 K3500 7.4l L29 4l80e 4 10 rear, hits all the gears and semi locks up when it should on acceleration, then when you get out of the throttle to maintain your speed it falls out of lockup.

It's like you reduced the throttle to 0 and lockup releases, but it happens about 10% throttle.

I setup two PIDs in torque pro to investigate, one monitors the gear it's in the other is TCC slip rpms. I first thought it was falling out of 4th gear but found out it's staying in 4th when this happens. It would never fully loch with a slip of 200~ rpm, then if you apply power it creeps up to 700ish before fully kicking down for power.

I was convinced I would need to go thru the 190000 mile trans, then I got it out on it's first road trip (for me) yesterday and found out it kinda has a second lockup that brings the slip to 0 or .5 rpm or some other acceptable number under 5 rpm slip. It's like it has a 2 stage TCC event.

So I'm basically piss ignorant on this 4l80e platform, but I'm suspecting a pressure regulator or solenoid/PWM issue.

Any suggestions are welcome. The trans internal harness was replaced before I get the truck so I'm assuming the grit was cleaned from the pan. Also it's not an intermittent issue, it screws up reliably.

Thanks for looking
Oldude

 

[ak diesel driver]

May not be the issue but the TCC lockup is also dependent on temperature, both engine and transmission.

 

[Oldude]

@ak diesel driver

It actually does the same cold and at op temp. You have to keep your foot in the throttle a little to keep it locked even at it's first "stage" at any temp.

Also forgot to mention, the TPS voltage is stable. I even tried a different TPS just to verify.

 

[ak diesel driver]

Yes but what numbers does the pcm see? IIRC it takes 170* before it locks up.

 

[Twisted Steel Performance]

And the tps needs to be adjusted right. Voltage should be .5, or half a volt at idle.

 

[Oldude]

I'll check both.

Right now we're prepping for 12deg nights, in Texas...

The distributor has been changed, twice before I got it. Not sure if it has been "timed". Might that be a factor? Also crank position sensor has been changed before I got it.

 

[ak diesel driver]

IIRC some engine codes won't let it lock up either

 

[Oldude]

Not getting any codes set but it does fail TID$07

Screenshot from torque pro: